The present invention relates to a method for manufacturing light-emitting device on non-transparent substrate, especially to a method for manufacturing light-emitting device on non-transparent substrate with high efficiency, better forward illumination and enhanced heat dissipation effect.
The nitride compound such as gallium nitride (GaN) is a direct band-gap material with energy gap corresponding to photon energy of green light and blue light. Therefore, the nitride compound is under extensive research to provide blue light source and green light source with higher efficiency and more practical application.
As to the material of substrate, sapphire has the advantage of good stability in high temperature condition during epitaxial growth process. However, the GaN film has relatively high lattice mismatch (16%) with underlying-sapphire substrate. To alleviate the effect of lattice mismatch, a GaN buffer layer is firstly grown on the sapphire substrate with a relatively low temperature (450-800xc2x0 C.). The GaN buffer layer is quasi epitaxial layer and has profound effect on growth of successive epitaxial layer and device performance. Afterward, an n-type GaN layer with thickness 3-4 mm is grown at 1000xc2x0 C. and an InGaN multiple quantum well active layer is grown at 600-900xc2x0 C., wherein the number of quantum wells is 4 to 10. After, a p-type GaN layer with thickness is grown again at 1000xc2x0 C. Finally, aside and n-side contacts are manufactured to complete the light-emitting device.
However, in above-mentioned light-emitting device, the p-side and n-side contacts are manufactured at the same face opposite to the sapphire substrate due to the electrical insulation of the sapphire substrate. The effective light emitting area is limited. Moreover, the sapphire has high hardness rendering the difficulty for slicing.
Alternative, a silicon substrate has the advantages of fewer defect, higher electrical conductivity, and lower price for larger area. However, the silicon substrate is a light absorbing material to reduce external quantum efficiency.
It is an object of the present invention to a method for manufacturing light-emitting device with higher efficiency.
It is another object of the present invention to a method for manufacturing light-emitting device with higher heat dissipation effect.
It is still another object of the present invention to a method for manufacturing light-emitting device with better forward illumination.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: